The present invention relates in general to cassette tape players, such as audio cassettes, and more specifically to detecting blank sections on a cassette tape not containing a recorded program information signal or to detecting blank moments in any signal medium containing gaussian noise.
Recorded cassette tapes typically contain blank unrecorded or silent sections between selections (songs) and at the end of one or both sides of the tape. The prior art attempts to detect blanks so that when a blank is encountered during playback that is longer than a predetermined period of time the cassette player automatically fast-winds the cassette tape to the end of the blank (or the end of the tape), providing a feature known as automatic blank skip. The prior art has also detected a blank versus a recorded section of the tape when in automatic music search mode, i.e., when the cassette player fast-winds through recorded sections to find the beginning of a desired selection on the tape as identified by its preceding blank.
Prior art identification of a blank is accomplished using a fixed voltage level detector. Specifically, the signal from a tape transducer head is amplified and rectified. When the absolute magnitude (peak or averaged) tape signal is less than a fixed threshold, a blank is detected. An inherent difficulty with this blank detection scheme is that a blank section of tape with a high noise floor is not detected as a blank. Further, a section of tape with a weak or low level program signal (i.e., music, voice, etc.) is detected as a blank. Because of unreliable blank detection, cassette players with automatic blank skip have required a skip control button to override inappropriate autowinding initiated during a nonblank tape section.